This invention relates to sorbent filter devices for removing contaminants from a confined environment such as computer disk drives and other electrical or optical devices.
Many electronic and/or optical devices are extremely sensitive to environmental contaminants particularly if the contaminants are gaseous in nature. Typically, the enclosures containing these sensitive devices are sealed, however, not hermetically sealed. Even if hermetic sealing were attempted, the devices would still be subjected to internally generated contaminants from out-gassing. As such, there is a need to remove harmful gaseous contaminants, whether the contaminants be internally generated to externally infiltrate into the enclosures, and whether the contaminants are organic, corrosive vapors, moisture, or the like. Also, as these devices are often small with limited available space it is desirable to provide sorbent filters which are small, yet can fit in available spaces and not shed particulates. It is known in the art to employ sorbent "breather" filters in enclosures of the above type. Known approaches to breather filters are discussed in U.S. Pat. No. 5,500,038 which states
"Sorbent breather filters used to keep particulates and vapors from entering enclosures are well known. These can be made by filling a cartridge of polycarbonate, acrylonitrile butadiene styrene (ABS), or similar material with sorbent and securing filter media on both ends of the cartridge. Examples of such filters are described in U.S. Pat. No. 4,863,499 issued to Osendorf, (an anti-diffusion chemical breather assembly for disk drives with filter media having a layer with impregnated activated charcoal granules); U.S. Pat. No. 5,030,260, issued to Beck et al. (a disk drive breather filter including an assembly with an extended diffusion path); U.S. Pat. No. 5,124,856, issued to Brown et al., (a unitary filter medium impregnated with activated carbon fibers to protect against organic and inorganic pollutants)." PA1 a) providing porous flexible tubular web structure having two open ends; PA1 b) sealing a first end of the tubular web structure; PA1 c) filling the sealed tubular web structure with flowable filter material or sorbent material and binder; PA1 d) sealing the opposite open end of the tubular web material; and PA1 e) heating the filled and sealed tubular web structure to activate the binder and form a shaped sorbent filter.
This patent goes on to indicate that these known types of breather filters are unacceptable. The patent further describes the prior art approach of U.S. Pat. No. 4,830,643 where granular absorbent materials are filled in an expanded polytetrafluoroethylene tube (PTFE). This approach is also criticized in the '038 patent for a number of reasons including the possibility that the loose fill can be spilled if the container tube is broken. As such, the '038 patent proposes starting with a sorbent core material where the sorbent particles are immobilized by being held in a matrix, such as an impregnated nonwoven molded article with a binder or a sorbent particle filled polytetrafluoroethylene sheet. The immobilized carbon is then overwrapped, such as by a cigarette wrap, or filled into a preformed tube where end seals are provided by a potting technique.
A similar approach is proposed in PCT Appln. WO 98/41989, which proposes a shaped molded carbon article formed by compression molding a particulate absorbent with a mixed-in binder. The compression molded tablet or brick of absorbent material and binder can then be placed in a preformed container or pouch.
Compression molded or otherwise immobilized carbon particles, and other sorbents, formed into a preformed structure is well known in other fields as well. For example, in U.S. Pat. No. 3,474,600 (Tobias) molded tablets of absorbent carbon are formed under heat and pressure to form cigarette filters or cylindrical material for use in packed beds; U.S. Pat. No. 4,665,050 (Degen et al.) describes a specific process for molding sorbents with a binder to form monolithic shapes such as cylinders, a similar approach is also described in U.S. Pat. Nos. 4,664,683; 5,033,465 and 5,078,132 describe shaped structures formed by immobilized carbon, such as filter cakes for use in respirators; U.S. Pat. No. 5,332,426 describes forming various shaped structures from agglomerated sorbent granules where the agglomerate granules are formed with a plurality or sorbent particles which agglomerates are subsequently formed into structures by bonding together the agglomerates with the binder particles of the agglomerates; U.S. Pat. No. 3,091,550 describes forming a monolithic structure of activated carbon by use of emulsion binder or a binder suspended in an aqueous emulsion; U.S. Pat. No. 4,386,947 describes forming a extrudable dough-like mixture of activated carbon blended with a cellulosic material, water, varnish and an imide resin, where the dough is formed into a predetermined structure and heated to form a monolithic structure; U.S. Pat. No. 4,061,807 describes distributing a binder on an absorbent by mixing in a small amount of water, which is formed into a monolithic structure in a mold and is subsequently heated to drive off the water and activate the binder, UK Pat. 1,390,668 describes forming a variety of shapes by mixing a heated adsorbent with a binder forming the predetermined structure followed by a subsequent heating step to set the binder. Monolithic sorbent particle structures as such are very well known in the art. Often, the formed monolithic structures of sorbent particles and binders are subsequently overwrapped to contain any flaked off particles or the like, such as described in U.S. Pat. No. 5,500,038 and PCT WO 98/41989. This provides a further level of security, which is desirable where carbon or other particles are potentially extremely dangerous, such as in sensitive electronic components or where carbon or other particles can present a health concern. However, it is often quite difficult to overwrap a structure in a manufacturing process, particularly where the overwrap must necessarily cover all portions of the formed structure. Generally, where overwrapping is done, the monolithic structures are simple blocks or other symmetrical linear structures for ease of manufacture. However, with electronic enclosures such as disk drives and the like, the available space is generally quite limited and it is frequently desirable to provide for sorbent filters of complex shapes to take up as much available space as possible, or to take full advantage of the available space, or provide desirable flow patterns. As such, the invention is directed at a novel method of forming complex shaped sorbent filters of overwrapped immobilized sorbents in a simple and economical manner.